The cleaning of skin with surface-active cleaning preparations has become a focus of great interest. Many people wash and scrub their skin with various surface active preparations several times a day. Liquid cleansers are highly preferred, especially for the body, because of convenience and non-messiness. Antibacterial personal cleansers are preferred because they kill germs. Mild personal cleansers are desired to minimize skin irritation, dryness, etc. A personal cleansing product having all three of these preferred characteristics would be very desirable.
Skin cleansers should cleanse the skin gently, causing little or no irritation, without drying the skin after frequent routine use. Certain synthetic surfactants are particularly mild. However, a major drawback of mild liquid synthetic surfactant systems when formulated for skin cleansing is poor lather performance. Compared to the highest bar soap standards (bars which are rich in coconut soap and superfatted), these prior art liquid surfactant formulations have either poor lather or poor skin mildness performance. As may be expected, the lather performance is a function of the choice of surfactant and its concentration. The conceivable number of liquid surfactant compositions formulated with or without skin feel agents are numerous. Rheological and phase properties exhibited by prototypes vary widely (i.e., thin liquids, gels, thick pastes, solutions, emulsions). The phase stability of prototypes is for the most part acceptable over short time periods, but only a small fraction of them will maintain their original properties and acceptability over an extended period of time. See, e.g., U.S. Pat. No. 4,338,211, Stiros, issued Jul. 6, 1982; U.S. Pat. No. 4,310,433, Stiros, issued Jan. 12, 1982; and U.S. Pat. No. 4,842,850, Vu, issued Jun. 27, 1989, all of said patents being incorporated herein by reference.
Optimization of lather as a single variable is a fairly straightforward process. The use of known high sudsing anionic surfactants with lather boosters yields acceptable lather volume. Unfortunately, highest sudsing anionic surfactants are, generally, also highest in skin irritation and are worst in clinical mildness. Surfactants that are among the mildest with minimal skin irritation, such as ammonium lauryl ether (12 EO) sulfate (NH.sub.4 AE.sub.12 S) are extremely poor in lather. These two facts alone make the surfactant selection and the lather boosting optimization process a delicate balancing act. See, e.g., U.S. Pat. No. 4,338,211, supra, incorporated herein by reference.
The introduction of an antibacterial into the equation results in additional problems for mildness, lather, and efficacy. It is reported in trade literature that certain mild ethoxylated nonionic surfactants, e.g., TweenR 80 (ICI Americas, Inc.) and lecithin have deactivating effects on the degerming of a preferred antibacterial, Triclosan (IrgasanR DP 300 is also referred to herein as "TCS"), Ciba-Geigy IrgasanR DP 300 Trade Bulletin, 1988.
In short, there are rather stringent requirements for skin cleansers which limit the choice of surface-active agents and antibacterials, and as a result the degerming final formulations represent some degree of compromise. Mildness is often obtained at the expense of effective degerming or effective cleansing and lathering which may be sacrificed for either mildness, product stability, or both.
The present invention offers a valuable combination of desirable properties to liquid skin-cleaning formulations.
Therefore, one object of this invention is the development of liquid skin cleaning compositions which exhibit improved mildness with good cleaning and lathering, and good degerming properties.
Other objects will become apparent from the detailed description below.